Hermaphrodites
Pat Loughlin
according to evolutionary theory? Seems like a hermaphrodite species
could achieve most of the advantages of a diverse gene pool (assuming
the individual can not mate with itself) while being much more
efficient with resources.
Pat
Name And Address Supplied
Why more efficient? Surely specialists are more efficient than generalists?
Tim Tyler
: Does anyone know why there are not more hermaphrodite species,
The question of why the sexes are divided is addressed in chapter four of
"The Red Queen" - by Matt Ridley.
Some other explanations have also been proposed - Wirt Atmar's
explanation, and the hypothesis that the different male and
female strategies are best off in whole sexually dimorphic
organisms.
The last theory might help explain why there are more hermaphrodite
plants than animals - since scattering strategies and
mobile organisms make a good match.
--
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|im |yler http://timtyler.org/ t...@tt1.org
Wirt Atmar
This is a very reasonable question, but given the paucity of obligately outbred
hemaphroditic species in nature, evolution must clearly have found substantial
advantage in the invention and exaggeration of gender.
The reason for that invention may lie in a completely unexpected answer: the
suppression of germline error. The rates of error infusion into germline DNA
are not trivial. Without the invention of mechanisms to identify that error and
expunge it from the germline, that error will only continue to accumulate,
constantly degrading the competitiveness of the species until finally it
reaches the point of quiescing the species's capacity to continue.
The only universal criterion that can be used to identify the male gender is
the size of its gametes. When anisogamy (differently sized gametes) is present,
as it is in virtually all plant and animal species, the smaller gametic gender
is declared the male. This smaller size intrinsically allows the male gender to
produce more gametes, spread them more widely, and tolerate more failures to
inseminate an egg, simply because the "investment" in any one gamete is so much
smaller than that of the macrogametic gender's investment in its eggs.
But this difference in gametic investment also allows evolution to exaggerate
gender-specific differences in the behavior of the adult male as well, making
it inherently more error expositive, more sacrificial and more combative than
the species's female. By doing this, the species appears to be testing the
male's lack of primary congenital defects prior to mating, allowing the male to
act as an filter of gene defects without imposing an equal cost on the
mother-daughter line of descent.
If you wish to read more on this form of explanation, please see:
http://aics-research.com/research/males1.html
The rate of error infusion into a germline is not trivial. If the species is to
outlive its cells, then some mechanism of error identification and expurgation
must be invented and imposed on the transmission of germline DNA, generation to
generation. If the species remains hermaphroditic, then all individuals must be
forced to run some sort of gauntlet to demonstrate their absence of significant
congenital defects prior to mating. But if the species partitions itself into
two gender castes, then only one of those genders need be put at substantial
risk in order to demonstrate its lack of defects.
Wirt Atmar
Michael Ragland
Wirt Atmar
Interesting article you wrote. I understood the "general points" but I
did not understand the more technical sections. You write, "The rate of
error infusion into a germline is not trivial. If the species is to
outlive its cells, then some mechanism of error identification and
expurgation must be invented and imposed on the transmission of germline
DNA, generation to generation." By nature creating a "male sex" this
acts to suppress germline error. As you state, "The difference in
gametic investment allows evolution to exaggerate gender-specific
differences in the behavior of the adult male as well, making it
inherently more error expositive, more sacrificial and more combative
than the species's female. By doing this, the species appears to be
testing the male's lack of primary congenital defects prior to mating,
allowing the male to act as an filter of gene defects without imposing
an equal cost on the mother-daughter line of descent." I'm not a
biologist but I agree with you.
This raises some interesting questions. Assuming nature created the male
sex and this suppressed germline errors (which I think is the case)
obviously it was not capable of eliminating germline errors. I would
argue that was not nature's intention. Theoretically, if all germline
errors were eliminated (as opposed to suppressed) the error
expositiveness, sacrificiality, and combativeness (competing for mating
rights to the female) would not exist. So, the creation of the male sex
was to suppress germline errors but never to eliminate them.
Although genetic engineering is in its early development arguably
eventually it will be able to remove many genetic diseases from the
germline. This is something which the male sex arguably would never be
able to do through suppression of germline error. The question arises
how genetic engineering of humans will influence and effect the two
sexes.
Michael Ragland
Stephen Hawking quotes from Larry King LIve Weekend December 25, 1999,
9:00 ET
"I think the biggest challenge we face is from our aggressive instincts.
In caveman -- or caveperson days, these gave definite survival
advantages and were imprinted in our genetic code by Darwinian natural
selection. But with nuclear weapons, they threaten our destruction. We
don't have time for Darwinian evolution to remove our aggression. We
will have to use genetic engineering."
"I think genetic engineering with humans is going to occur whether we
like it or not. It will change our standard of what is human but it will
be a gradual change because there's so much we don't know and because
humans take time to grow up. We won't change much in the next 100 years
but we might after that."
Pat Loughlin
Thanks for the response. I read your paper. I am not a biologist but
was able to understand most of it. I think a misconception I had from
my high school biology class was that an error in a gene would result
in the elimination of some trait in the individual. What I understood
from your paper was that an error in a gene would most likely result
in slight decrease in trait, not its elimination. This makes more
sense. And thus this slight decrease would only be exposed and
eliminated through some vigorous contest among the males.
Pat